Stirring device for activated sludges

ABSTRACT

The invention relates to a stirring device for activated sludges comprising a hyperboloid stirring body ( 1 ) attached to a shaft ( 2 ), wherein a plurality of transport ribs ( 3 ) are provided on the top (O) of the stirring body ( 1 ) running toward the circumferential boundary (UM) thereof, wherein the transport ribs ( 3 ) have an oblique course, at least in sections, relative to a radial direction, and wherein the oblique position of the transport ribs ( 3 ) is selected such that, when the stirring body ( 1 ) rotates in a predetermined rotational direction (R), a flow (S) is generated that is directed outward away from the circumferential boundary (UM) of the stirring body ( 1 ). In order to improve the efficiency of the stirring device, the invention proposes that a flow guidance device ( 7 ) for guiding the flow (S) generated by the stirring body ( 1 ) be provided in a plane running substantially perpendicular to the shaft ( 2 ), said flow guidance device surrounding the circumferential boundary (UM) of the stirring body ( 1 ) and being relatively fixed thereto.

The invention relates to a stirring device for activated sludges as defined in the preamble of claim 1.

Such a device is known, for example, from DE 42 18 027 A1 or DE 198 26 098 C2. With the known stirring device, a hyperboloid-like stirring body is attached to a shaft. A plurality of transport ribs running radially inclined are provided on the upper side of the stirring body. During a rotation of the stirring body, a flow directed away from the circumferential boundary of the stirring body is generated in a liquid medium surrounding the stirring body due to its hyperboloid-like shape as well as due to the effect of the transport ribs.

The invention is based on the object of specifying a stirring device with improved stirring efficiency.

This object is solved by the features of claim 1. Useful embodiments result from the claims 2 to 14.

According to the provisions of the invention, a flow guiding device which surrounds the circumferential boundary of the stirring body and which is relatively fixed thereto is provided to guide the flow generated by the stirring body in a plane running essentially vertically to the shaft. This improves the stirring efficiency in a simple and inexpensive manner.

The invention is based on the finding that the stirring efficiency increases with an increasing radial range of the flow directed away from the circumferential boundary of the stirring body. It has been observed that, due to the flow below the stirring body, a not insignificant suction develops which causes a backflow opposite to the flow. The backflow slows the flow and inhibits the development of a wide radial range of same.

The flow guiding device suggested by the invention guides the flow generated by the stirring body in a plane running essentially vertically to the shaft and counteracts in particular the formation of flow components directed inclined towards the bottom of the basin. A mutual interaction of the flow and the backflow is diminished. This can significantly improve the radial range of the flow.

The transport ribs usefully form a first angle of inclination of −30° to −90°, preferably of −40° to −80°, with the radial direction at least in the area of the circumferential boundary. The negative sign used in front of the amount of the previously stated first angle of inclination indicates that this first angle of inclination opens in the direction opposite to the direction of rotation with respect to the radial direction.

In an advantageous embodiment, the flow guiding device has an annular gap surrounding the circumferential boundary which gap is formed by lower and upper flow conducting means arranged coaxially to the shaft. The flow conducting means can be flat elements, made of plastic, in particular of fiber-reinforced plastic, or also of metal, preferably of stainless steel. The flow guiding device usefully forms a mounting unit. For this purpose, the upper and lower flow conducting means can be connected to each other via means of connection. The means of connection can be essentially radially running walls. The provision of such walls contributes to an improved flow guidance in the radial direction and thus further increases the range of the flow.

In an alternate embodiment, the means of connection are first inclined walls, running inclined with respect to the radial direction which form a second angle of inclination of +30° to +90°, preferably of +40° to +80°, with the radial direction. The positive sign used in front of the amount of the previously stated second angle of inclination indicates that the second angle of inclination opens in the direction of rotation with respect to the radial direction. The second angle of inclination is in particular selected in such a way that it is essentially directed parallel to the flow generated by the stirring body. Consequently, a diversion of the flow is avoided. The radial range of the flow can thus be further improved.

In a further embodiment, the lower flow conducting means is a ring disk extending essentially parallel to the plane. A breakthrough provided in the center of the ring disk enables the passage of the liquid medium on the bottom of the basin flowing back to the operational area of the stirring body and thus its acceleration in a radial direction pointing to the outside.

Support elements for support on a bottom of the basin can be provided on an underside of the lower flow means pointing away from the upper flow means such that a further annular gap is formed between the bottom and the lower flow means. The further annual gap enables the essentially unhindered development of the backflow in an area below the stirring body.

The means of support can essentially be radially running, further walls. Such further walls provide a low flow resistance to the backflow, thus contributing to the development of a flow with an improved range.

In an alternate embodiment, the means of support are second inclined walls running inclined with respect to the radial direction which form a third angle of inclination of −30° to −90°, preferably of −40° to −80°, with the radial direction. The negative sign in front of the amount of the previously stated third angle of inclination indicates in turn that this angle opens in a direction opposite to the direction of rotation of the stirring body with respect to the radial direction. The suggested inclination of the second inclined walls is in particular selected so that it runs parallel to the direction of a backflow near the bottom. A diversion of the backflow is thus avoided. Consequently, the backflow is exposed to as slight a resistance as possible, whereby the radial range of the flow can in turn be increased.

In a particularly advantageous embodiment, a gap width of the annular gap running essentially parallel to the shaft expands towards the circumferential boundary of the stirring body. In this case, the annular gap forms a ring nozzle with which the flow directed away from the circumferential boundary of the stirring body is not only guided in a plane essentially parallel to the bottom of the basin but is also accelerated in this plane. This significantly contributes again to the improvement of the radial range of the flow.

The transport ribs can bend towards the circumferential boundary from an approximately radial direction in an approximately tangential direction directed opposite the direction of rotation. Moreover, they can only extend in an outer radial section of the upper side. In this embodiment, a flow directed away from a circumferential boundary of the stirring body can be generated with a particularly high speed.

In a further embodiment, a plurality of essentially radially running shear ribs is provided on a further underside located opposite the upper side. A height of the shear ribs can increase towards the circumferential boundary of the stirring body. Such shear ribs are used to distribute the air which can be supplied in via an air supply line to the area below the stirring body. With this, the liquid medium surrounding the stirring body can not only be transported efficiently with a wide range in a radial direction but it can also be mixed with very fine air bubbles.

The invention will now be described in more detail using an example based on the drawing:

FIG. 1 a partial cross sectional view of a stirring device,

FIG. 2 a complete cross sectional view of the stirring device in accordance with FIG. 1,

FIG. 3 a perspective view of the stirring device and

FIG. 4 a top view of a further stirring device.

FIG. 1 shows a side view of a hyperboloid-like stirring body 1 which is attached to a shaft 2. Transport ribs 3 are provided on an upper side O of the stirring body 1 in a radially outer section which ribs extend up to a circumferential boundary UM. The transport ribs 3 initially run in an essentially radial direction and then bend in a direction opposite the direction of rotation R in an essentially tangential direction. On an underside U shear ribs 4 are provided in the vicinity of the circumferential boundary UM whose height increases in a direction pointing radially to the outside. As is particularly apparent in FIG. 2, the stirring body 1 is formed from a hyperboloid-like shaped stirring body wall 5. Thus it has a funnel-like recess 6 on its underside U.

As is shown in FIGS. 1 to 3, the circumferential boundary UM of the stirring body 1 is surrounded by a flow guiding device 7. The flow guiding device 7 comprises a lower ring disk 8 and a ring disk-like flow conducting element 9 located above, which is held at a distance from the ring disk 8 via radially running walls 10. An annular gap 11 is formed between the ring disk 8 and the flow conducting element 9 which surrounds the circumferential boundary UM. The flow conducting element 9 is bent upward in a direction pointing towards the shaft 2 so that the annular gap 11 expands in a direction towards the circumferential boundary UM. The ring disk 8 is supported via further walls 12 which are also arranged essentially radially on a bottom B of a basin (not completely shown here). A height of the further walls 12 defines a further annular gap 13 between the bottom B and the ring disk 8.

The function of the stirring device is as follows:

A flow S pointing to the outside away from the circumferential boundary UM is generated in particular by the action of the transport ribs 3 via a rotation of the stirring body 1 in the direction of rotation R. The flowing, liquid medium, for example sewage sludge, waste water or similar, is forced through the annular gap 11. Due to the diminishing cross section of the annular gap 11, the flowing medium is accelerated. Aside from that, the flow S is forced in a direction which essentially runs parallel to the bottom B.

As a result of the developing flow S, a suction is generated below the stirring body 1 which suction in turn generates a backflow RS in the opposite direction to the flow S. The backflow RS which is also essentially directed parallel to the bottom B enters the flow guiding device 7 through the lower annular gap 13 and is then diverted by the action of the stirring body 1 in order to leave the annular gap 11 again with the flow S.

Air can be supplied to the recess 6 via an air supply line (not shown here). The air supply line can extend essentially parallel to the bottom B and bend below the shaft 2 in the direction of the recess 6. The medium flowing back as per the backflow RS can be mixed with the supplied air via the shear ribs 4 while exiting through the annular gap 11. A liquid medium then exits through annular gap 11 which contains very fine air bubbles.

With the suggested flow guiding device 7 the flow S and the. backflow RS are guided in parallel planes located on top of each other. This decreases interactions between both flows S, RS. A radial range of the flow S and thus the efficiency of the stirring device are improved.

FIG. 4 shows a top view of a further stirring device. To the extent that the components of the further stirring device are identical or essentially similar to the components of the stirring device shown in FIGS. 1 to 3, the reference signs used there have been used. Reference sign a designates a first angle of inclination which is formed between a section of the transport ribs 3 in the area of the circumferential boundary UM and a radial direction RR. The first angle of inclination α is in an area from −30° to −90°, here approximately at −45°.

The further stirring device differs from the stirring device shown in FIGS. 1 to 3 essentially in an inclination of the walls 5 as well as of the further walls 12. First inclined walls 10 a are suggested in FIG. 4 with long broken lines. They connect the flow conducting element 9 with the ring disk 8 arranged underneath. With a radial direction RR, the horizontally running first inclined walls 10 a form a second angle of inclination β of +30° to +90°, here approximately +45°. Second inclined walls 12 a support the ring disk 8 against the bottom B. Together with the radial direction RR, the also horizontally arranged second inclined walls 12 a form a third angle of inclination γ in the area of −30° to −90°, here approximately −45°.

As indicated in FIG. 4, the first inclined walls 10 a run approximately vertically to the second inclined walls 12 a. The flow S generated by the stirring body 1 runs approximately parallel to the first inclined walls 10 a. The backflow RS runs approximately parallel to the second inclined walls 12 a.

As further indicated in FIG. 4, in particular the first inclined walls 10 a are not parallel arranged to each other. An annular gap section created by the first inclined walls 10 a widens in the radial direction. Consequently, the speed of the flow decreases in the radial direction due to the annular gap section. To counteract this disadvantage and achieve a particularly wide range of the flow S, an auxiliary wall 10 b can be provided in a further embodiment which wall runs parallel to the first inclined wall 10 a arranged opposite the direction of rotation R and which has a common edge with the next first inclined wall 10 a in the vicinity of the circumferential boundary UM. With this embodiment, it is achieved that an entry area of an annular gap section in the vicinity of the circumferential section UM corresponds approximately to an exit area of the annular gap section. With this, a slowdown of the flow S during the passage through the annular gap 11 can be avoided.

LIST OF REFERENCE SIGNS

1 Stirring body

2 Shaft

3 Transport rib

4 Shear rib

5 Wall

6 Recess

7 Flow guiding device

8 Ring disk

9 Flow conducting element

10 Wall

10 a First inclined wall

10 b Auxiliary wall

11 Annular gap

12 Further wall

12 a Second inclined wall

13 Further annular gap

O Upper side

UM Circumferential boundary

U Underside

R Direction of rotation

S Flow

RS Backflow

B Bottom

RR Radial direction

α First angle of inclination

β Second angle of inclination

γ Third angle of inclination 

1. Stirring device for activated sludges comprising a hyperboloid-like stirring body (1) attached to a shaft (2), wherein on an upper side (O) of the stirring body (1) a plurality of transport ribs (3) running towards its circumferential boundary (UM) is provided, wherein the transport ribs (3) are running inclined at least in sections with respect to a radial direction and wherein a first inclination of the transport ribs (3) is selected in such a manner that, when the stirring body (1) rotates in a predetermined direction of rotation (R), a flow (S) directed away from the circumferential boundary (UM) of the stirring body (1) to the outside is generated, characterized in that a flow guiding device (7) which surrounds the circumferential boundary (UM) of the stirring body (1) and which is relatively fixed thereto is provided to guide the flow (S) generated by the stirring body (1) in a plane running essentially vertically to the shaft (2).
 2. Stirring device as defined in claim 1, wherein the transport ribs form a first angle of inclination (α) of −30° to −90°, preferably of −40° to −80°, with the radial direction at least in the area of the circumferential boundary (UM).
 3. Stirring device as defined in claim 1 wherein the flow guiding device (7) has an annular gap (11) surrounding the circumferential boundary (UM) which is formed by lower and upper flow conducting means arranged coaxially to the shaft (2).
 4. Stirring device as defined in claim 1 wherein the upper and lower flow conducting means are connected to each other via means of connection.
 5. Stirring device as defined in claim 1 wherein the means of connection are essentially radially running walls (10).
 6. Stirring device as defined in claim 1 wherein the means of connection are first inclined walls (10 a) running inclined with respect to the radial direction which form a second angle of inclination (β) of +30° to +90°, preferably of +40° to +80°, with the radial direction.
 7. Stirring device as defined in claim 1 wherein the lower flow conducting means is a ring disk (8) extending essentially parallel to the plane.
 8. Stirring device as defined in claim 1 wherein support elements are provided on an underside of the lower flow conducting means pointing away from the upper flow conducting means (9) for support on a bottom (B) of a basin in such a manner that a further annular gap (13) is formed between the bottom (B) and the lower flow conducting means.
 9. Stirring device as defined in claim 1 wherein the means of support are essentially radially running further walls (12).
 10. Stirring device as defined in claim 1 wherein the means of support are second inclined walls (10 b) running inclined with respect to the radial direction, which form a third angle of inclination (γ) of −30° to −90°, preferably of −40° to −80°, with the radial direction.
 11. Stirring device as defined in claim 1 wherein a gap width of the annular gap (11) running essentially parallel to the shaft (3) expands towards the circumferential boundary (UM) of the stirring body (1).
 12. Stirring device as defined in claim 1 wherein the transport ribs (3) bend towards the circumferential boundary (UM) from an approximately radial direction in an approximately tangential direction directed opposite the direction of rotation (R).
 13. Stirring device as defined in claim 1 wherein the transport ribs (3) only extend in an outer radial section of the upper side (O).
 14. Stirring device as defined in claim 1 wherein a plurality of essentially radially running shear ribs (4) is provided on a further underside (U) located opposite the upper side (O).
 15. Stirring device as defined in claim 1 wherein a height of the shear ribs (4) increases towards the circumferential boundary (UM) of the stirring body (1). 